A vehicle may include an electric machine to provide propulsive torque to accelerate the vehicle. The electric machine may also provide a braking torque to the vehicle whereby the vehicle's kinetic energy may be converted into electric energy and stored for subsequent use. The electric machine may be electrically coupled to a battery or other electric energy storage device via an inverter. The inverter may convert direct current (DC) from the battery into alternating current (AC) to power the electric machine. Alternatively, the inverter may convert alternating current into direct current to charge the battery. The inverter may include a buck circuit and a boost circuit to increase battery voltage or decrease electric machine voltage. For example, when the inverter operates in a boost mode, battery voltage may be increased via storing electric energy in a magnetic field of an inductor and then discharging the inductor to the electric machine. The voltage developed across the inductor plus the battery voltage results in an output voltage that is greater than battery voltage. However, if the voltage output from the battery and the inductor is above or below a desired voltage where the electric machine operates efficiently, electrical power use by the electric machine may be less efficient than is desired.
The inventors herein have recognized the above-mentioned issues and have developed a variable voltage control inverter operating method, comprising: receiving data to a controller; and switching a transistor of the variable voltage control inverter at a duty cycle via the controller in response to a desired output voltage of the variable voltage control inverter not being less than a battery voltage, the duty cycle adjusted responsive to the battery voltage.
By switching a transistor of a variable voltage control inverter at a duty cycle that is responsive to battery voltage when a desired output voltage of the variable voltage control inverter is not less than battery voltage, it may be possible to provide the technical result of improving electrical system efficiency. In particular, efficiency of an electric machine may be improved. Further, if the inverter is operated on a buck mode, battery charging efficiency may be improved by precisely controlling battery charging voltage.
The present description may provide several advantages. In particular, the approach may reduce over boosting when battery charge is low. Further, the approach may increase battery voltage boost capability by allowing the inverter to boost to higher voltages. In addition, the approach may be applied while operating the inverter in buck or boost modes.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.